KOCK, Anders; KRISTENSEN, Leif. A Secondary Product Structure in Cohomology Theory. Mathematica Scandinavica, Berkeley, CA, United States, v. 17, p. 113–149, 1965. DOI: 10.7146/math.scand.a-10768. Disponível em: https://journals.msp.org/mscand/article/view/2556. Acesso em: 25 jul. 2026.